1. Field of the Invention
The present invention relates to a vehicle body speed estimating device, and in particular, to a vehicle body speed estimating device that estimates lateral vehicle body speed, or longitudinal vehicle body speed and lateral vehicle body speed, by an observer that includes a time-varying parameter, while focusing on the fact that, in a case in which lateral vehicle body speed or longitudinal vehicle body speed and lateral vehicle body speed are made to be the outputs of a motion equation of a rigid body, in which longitudinal vehicle body speed and lateral vehicle body speed are considered to be state amounts and the yaw angular velocity is considered to be a time-varying parameter that varies in accordance with time and is unrelated to the state amounts, the motion equation is an observable object of control.
2. Description of the Related Art
Estimation of a vehicle body slip angle that corresponds to vehicle body lateral speed is conventionally carried out on the basis of a lateral direction vehicle motion model in which the lateral force of the tire is described as a function of the slip angle of the tire. This vehicle motion model uses a motion equation in which the yaw angular velocity and the lateral speed or the slip angle are made to be state amounts. In most cases, the vehicle motion model structures an observer whose output is yaw angular velocity or lateral acceleration.
However, an actual vehicle motion model includes, as a model, the relationship between the slip angle and the lateral force of the tire. Accordingly, in a non-linear region in which the actual vehicle model and the vehicle model that is used do not coincide, complex correction by a correcting means is required, such as correcting the cornering power that is a parameter (Japanese Patent Application Laid-Open (JP-A) No. 62-83247), or switching to an integration technique that does not use a model (JP-A No. 8-332934).
Further, a technique for estimating unstable behavior of a vehicle (“Development of Technique for Estimating Unstable Behavior of Vehicle”, Shiozawa et al., Society of Automotive Engineers of Japan, JSAE Paper No. 20065708) is known as a conventional technique for estimating the slip angle on the basis of the longitudinal direction and lateral direction motions of the vehicle body. Based on the assumption that the acceleration that arises at a vehicle body coincides with centrifugal acceleration, this technique is a technique that estimates the direction of the centrifugal acceleration from the value of the longitudinal direction acceleration and the value of the lateral direction acceleration of the vehicle body, and estimates the slip angle from the estimated direction of the centrifugal acceleration.
However, in the techniques of aforementioned JP-A No. 62-83247 and JP-A No. 8-332934, it is not easy to appropriately carry out the above-described complex corrections. Further, if an integration method is continued for a long period of time, problems arise such as estimation is affected by drift errors of the in-vehicle sensors and the accuracy of estimation deteriorates, and the like.
Moreover, in the aforementioned technique of “Development of Technique for Estimating Unstable Behavior of Vehicle”, Shiozawa et al., Society of Automotive Engineers of Japan, JSAE Paper No. 20065708, because there is no need to use a vehicle motion model, there is the advantage that estimation is not affected by the road surface on which the vehicle travels. However, because this technique assumes that the acceleration that arises at the vehicle body coincides with centrifugal acceleration, there is the problem that the slip angle cannot be estimated accurately in a situation in which acceleration other than centrifugal acceleration arises, such as at the time of acceleration/deceleration of the vehicle or the like.